Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. For example, rotor blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is geared to a generator for producing electricity.
The lift force is generated when the flow from a leading edge to a trailing edge creates a pressure difference between the top and bottom surfaces of the blade. Ideally, the flow is attached to the top surface from the leading edge to the trailing edge. However, when the angle of attack of the flow exceeds a certain critical angle, the flow does not reach the trailing edge, but leaves the surface at a flow separation line, which decreases potential energy production.
Hence, in order to increase the energy conversion efficiency during normal operation of the wind turbine, it is desired to increase the lift force of the blades while decreasing the drag force. To this purpose, it is advantageous to increase the attached-flow region and to reduce the detached-flow region by moving flow separation nearer the trailing edge of the blade. As such, it is known in the art to change the aerodynamic characteristics of wind turbine blades by adding various add-ons and/or components on the surface of the blade. For example, such add-ons may generally include leading edge extensions, trailing edge extensions, vortex generators, blade root enhancements, bumps, winglets, airflow modifying elements, and/or any other suitable components.
The rotor blades and many of the add-ons are constructed of a fiberglass composite material due to their large size and typically require specialized tooling and/or molds for their manufacture. For example, the blade halves of a conventional rotor blade are typically formed in large molds that are custom made for the particular size and shape of the rotor blade being produced. More specifically, various rotor blades and/or rotor blade components may be constructed using Resin Transfer Molding (RTM), such as Vacuum Assisted Resin Transfer Molding (VARTM). With the VARTM process, composite parts are made by placing dry fiber reinforcing fabrics into a single part, open mold, enclosing the mold into a vacuum bag, and drawing a vacuum in order to ensure a complete preform infiltration with resin. The mold is then heated to allow the part to cure. The VARTM process makes it possible to produce relatively inexpensive, large, and complex parts in one shot.
Various issues associated with previous methods for manufacturing rotor blades, however, have been identified. For example, many of the RTM processes are time-consuming due to the required cure time for each part. In addition, since rotor blades are constantly moving and flexing in the wind, add-on parts also need to be flexible enough to move with the blade. However, thin fiberglass composite parts are typically inherently brittle and can resist movement of the rotor blades. In many instances, the thickness of the fiberglass parts can be increased to provide a more durable part, but such a modification also adds weight to the rotor blade. While some light-weight, flexible rotor blade components may be manufactured by coating a mold with an elastomeric material and filling it with foam, the foam may impart internal pressure on the mold and the elastomeric material while the foam fills and expands.
Accordingly, alternative methods of manufacturing rotor blade components would be welcomed in the art.